Thing that always got me was how many sinkholes are nearly perfect circles. One time a geologist tried to explain that to me and it depends on two things (1) the type of sinkhole has to be something called a “cover-collapse sinkhole” and (2) the void causing event, which is usually but not always, water dissolving/transporting, has to be a pretty significant ways down below and not close to the surface. Then you get a ‘dome’ formation which due to physics (isn’t everything?) will propagate upwards as a circular cave-in. …maybe.
(image source and article)
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